I find it’s best to tell yourself WHEN you’ll use those irreplaceable items when you get them. All of my masterballs have labels on them that say ‘Shiny Pokemon that flee’. Having every legendary be a bit tougher to get is nowhere near as painful as watching a shiny abra teleport away… I presume… Hundreds of hours in every game and I still only ever found one shiny.

Sensei Le Roof

I only recently encountered my first shiny. It was a Trapinch. … I accidentally killed it.

Triaxx2

Shinies or legendarys without a Smeagle. That’s what the Masterball is for. Except for Red/Blue. Then Mewtwo gets it to the face.